In co-pending application, Ser. No. 633,174 now U.S. Pat. No. 4,518,972, filed on even date herewith and titled "Graphics Plotter Turret Head" by co-inventor Charles Gunderson of this application and assigned to the common assignee of this application, there is disclosed a turret head for a graphics plotter wherein the turret head and an associated pen holder move with the pen carriage to provide exchangeability of eight pens adjacent the writing site. To assure failsafe, reliable and optimum operation of that turret head and the associated plotter, a control system and associated devices was necessary. Since the turret head described therein is of novel construction, no such associated control system and apparatus existed in the art for use in conjunction therewith. The present invention, therefore, relates to a control system and associated devices for use in conjunction with the aforementioned graphics plotter turret head as incorporated into a commercial graphics plotter by the common assignee of the two applications.